Line a 9x9x2-inch or 11x7x11/2-inch baking pan with foil, extending the foil over edges of pan. Butter the foil; set pan aside.

In a large microwave-safe bowl microwave the butter, uncovered, on 100 percent power (high) for 1 to 1-1/2 minutes or until melted. Stir in cocoa powder, brown sugar, and milk. Microwave, uncovered, on high for 1 to 2 minutes or until mixture comes to a boil, stirring once. Stir again; microwave for 30 seconds more. Stir in powdered sugar and vanilla until smooth. Spread in prepared pan.

In a medium microwave-safe bowl combine caramels and water. Microwave, uncovered, on 50 percent power (medium) for 2-1/2 to 3 minutes or until caramels are melted, stirring once. Stir in peanuts. Microwave, uncovered, on medium for 45 to 60 seconds more or until mixture is softened. Gently and quickly spread peanut mixture over fudge layer in pan.

In a 2-cup microwave-safe glass measure combine semisweet and milk chocolate pieces. Microwave, uncovered, on 50 percent power (medium) for 2 to 3 minutes or until melted, stirring once or twice. Spread over peanut layer. Score into pieces while warm. Cover and chill for 2 to 3 hours or until bottom is firm. Use foil to lift candy out of pan. Cut into pieces. Store tightly covered in the refrigerator for up to 3 weeks. Makes about 2-3/4 pounds (64 pieces).

In a medium saucepan melt butter over medium heat. Stir in cocoa powder, brown sugar, and milk. Bring to boiling. Remove from heat; stir in powdered sugar and vanilla. Spread in prepared pan. In another saucepan melt caramels with water over low heat; stir in peanuts. Gently and quickly spread over fudge layer in pan. In a small saucepan melt semisweet and milk chocolate pieces over low heat, stirring constantly. Spread over peanut layer. Continue as directed.